1. Field of the Invention
This invention relates to a recording and/or reproducing apparatus for recording/reproducing information signals on or from a magnetic tape according to a so-called helical scan system. More particularly, it relates to such recording/reproducing apparatus provided with a dynamic tracking head which is moved in a direction perpendicular to the recording track on the magnetic tape and which is controlled in movement so as to accurately trace a recording track by a movement controlling unit.
2. Description of the Related Art
In a helical scanning type VTR, control CTL signals are recorded on longitudinally extending recording tracks on the magnetic tape, and a phase servo is applied by way of tracking servo, based on the time difference between the playback CTL signals produced on tape reproduction and the reference signals.
Since the CTL signals are reference signals for capstan servo, a capstan motor cannot be phase-locked if the CTL signals cannot be reproduced during the reproduction (play) mode.
Meanwhile, depending on the environment in which a VTR is employed, it frequently occurs that a recording head for recording CTL signals on a magnetic tape, or a playback head for reproducing CTL signals from the magnetic tape, undergoes so-called clogging, in which case the image or sound recorded on the magnetic tape becomes unable to be reproduced. It is however desirable in such case that the sound or image can be reproduced as normally.
With a so-called 1-inch VTR, a capstan motor can naturally not be phase-locked if a magnetic tape free of CTL signals is reproduced. However, with such 1-inch VTR, since audio signals are recorded in the longitudinal direction of the tape, the sound may be reproduced, even although the sound pitch is changed on the order of e.g. 0.1%.
On the other hand, it is possible with the 1-inch VTR to reproduce video signals recorded in the helical direction of the tape with a dynamic tracking head (DT head) which is controlled to be moved in a direction at right angles to the recording tracks on the tape by a movement controlling unit so that, even if the magnetic tape is devoid of the CTL signals, the recording tracks can be traced correctly on rotation of the recording track. However, since the DT head is deflected within a limited extent, head jump is produced if the amount of deflection of the DT head reaches the limit point. If such head jump is produced, it may occur that a one-frame picture may be dropped, or plural frames of pictures be reproduced in a superimposed manner.
Since the CTL signals are employed in the conventional digital VTR for controlling the DT head, reproduction could be made satisfactorily despite dropout of CTL signals for picture dropout on the order of a 1-frame color picture. However, reproduction becomes impossible if the CTL signals are absent for a prolonged time period.
As for the digital audio signals, these signals are recorded in the helical direction, so that sound skipping may be inhibited by cross-fading on the occasion of DT head jumping. However. with the video signals, picture dropout OF Superposition occur unavoidably due to head jump.